Devise method overrides in User model

user.rb

# app/models/user.rb

class User

  has_many :email_addresses
  accepts_nested_attributes_for :email_addresses

  # ... association definitions and other methods

  # Define our overrides:

  def email_required?
    false
  end

  def will_save_change_to_email?
    false
  end

  def self.find_first_by_auth_conditions(warden_conditions)
    conditions = warden_conditions.dup

    # If "email" is an attribute in the conditions,
    # remove it and save to variable
    if email = conditions.delete(:email)
      # Search through users by condition and also by
      # users who have associations to the provided email
      where(conditions.to_h).includes(:email_addresses).where(email_addresses: { email: email }).first
    else
      # If "email" is not an attribute in the conditions,
      # just search for users by the conditions as normal
      where(conditions.to_h).first
    end
  end
end